TWO incidents are described, both involving bleed air ducts but in dissimilar aircraft with different engines. One incident concerned a Boeing 747–136 in which at just after the decision speed V1. a loud ‘bang’ was heard followed by severe vibration from all four thrust levers. The take‐off was continued normally and the aircraft rotated normally at Vr and entered the climb. The landing gear was not immediately retracted due to the possibility of burst tyres, however, shortly after the aircraft became airborne the No 4 engine generator failure warning lights illuminated, the engine oil temperature indication decreased off‐scale and the exhaust gas temperature (EGT) also reduced to a low reading. Suspecting an engine failure, the commander ordered the landing gear to be retracted. However, since the No 4 engine N1, N2 and fuel flow indications remained normal, the commander decided not to shut down the engine. As the aircraft climbed through 500 ft, the right wing overhead warning light illuminated. At a safe height the flaps and leading edge devices were retracted, control was transferred to the co‐pilot and the flight engineer, monitored by the commander, completed the wing overheat and single generator inoperative check lists. While these were being completed, Heathrow ATC advised that debris had been found on the runway. The commander decided to return to Heathrow and radio vectors were requested for fuel jettison.
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